There are examples in the prior art of systems for monitoring a laser welding process and providing an evaluation of the process. One such example takes the form of the U.S. Pat. No. to T. Webber 4,663,513 which discloses a system for monitoring a laser welding process. In that process, a laser is employed for delivering energy to a workpiece along a process path while producing plasma at a beam delivery point along the path. Infrared radiation from a point behind and in close proximity to the location of the beam delivery point is detected by a radiation detector. The radiation detector provides an analog temperature signal having a value which varies over time with changes in intensity of the received infrared radiation. The analog temperature signal is compared against a window range of acceptable temperatures including a fixed upper limit and a fixed lower limit. If the temperature signal is not within the window range, then the output of the laser process is rejected.
The system described above in the aforesaid patent is not a real time monitoring system. Instead, it monitors infrared radiation from a point behind the location of the beam delivery point. The infrared detector does not respond to ultraviolet or visible light emissions from the plasma itself so as to provide real time monitoring. Moreover, the system provides either a process rejection or acceptance depending upon whether the temperature signal has a value which is within the window range or is outside of the window range. Consequently, this is a pass-fail test.
The U.S. Pat. No. to Sciaky et al. U.S. Pat. No. 3,262,006 discloses a welding control system having a light sensitive probe incorporating an arrangement using fiberoptics to conduct illumination from an area adjacent a weld to a photo transducer disposed at a remote location. Also, an ultraviolet filter may be employed in the system to see through the flame portion of the weld arc to the inner plasma portion. The system is employed to maintain an electrode at a substantially constant distance from the workpiece. While presenting real time monitoring, there is no teaching of determining relative quality of the welding process.
The U.S. Pat. No. to Kearney 4,446,354 discloses a weld monitoring system employing fiberoptic delivery of incident radiation to a plurality of photo detectors. The photo detectors evaluate the weld by determining the relative spectral energy of various wavelengths. These energy levels are compared with single level guard bands or limits to provide a pass-fail test.